Back flow preventers are described by many different names include backflow valves, backwater valves and backflow preventers.  No matter what they are called, their primary job is to prevent contaminated water from flowing back into the potable water supply. They work by automatically sensing a reversal in water flow in the pipe and they automatically

An atmospheric vacuum breaker is one of many backflow devices, or backflow preventers, which prevent contaminated water from flowing back into the potable water supply. The atmospheric vacuum breaker is usually constructed of brass and it appears to be a 90-degree elbow construction with a hood on its top to allow air to enter the

  For additional protection against possible backflow into your basement, you could also add a floor drain backflow preventer.  Usually these are check valves which are inexpensive and easy to install.  What they are, basically, is a compressed rubber gasket with a floating ball mounted on a spring.  It is installed into the vertical pipe